ul·cer (?l?s?r)n.1. A lesion of the skin or a mucous membrane such as the one lining the stomach or duodenum that is accompanied by formation of pus and necrosis of surrounding tissue, usually resulting from inflammation or ischemia.2. A corrupting condition or influence.[Middle English, from Old French ulcere, from Latin ulcus, ulcer-.]American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.ulcer (??ls?) n1. (Pathology) a disintegration of the surface of the skin or a mucous membrane resulting in an open sore that heals very slowly. See also peptic ulcer2. a source or element of corruption or evil[C14: from Latin ulcus; related to Greek helkos a sore]Collins English Dictionary ? Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014ul?cer (??l s?r) n. 1. a sore on the skin or a mucous membrane, accompanied by the disintegration of tissue, the formation of pus, etc. 2. peptic ulcer. 3. any corrupting or disrupting condition, element, etc. [1350?1400; Middle English